To reduce regulated exhaust gas emissions, a catalytic converter is typically installed in the exhaust system of the engine. The effectiveness of the catalyst in transforming the exhaust emissions depends on a number of factors, but is most influenced by the temperature of the catalyst and the mass air flow past the catalyst. Catalytic conversion does not occur until the catalyst reaches a relatively high operating temperature. As the catalyst temperature rises past a threshold temperature, the catalyst begins to promote the reactions which convert the exhaust emissions. The catalyst is most efficient when it is functioning within an operating temperature range based on the particular formulation and design of the catalyst.
When the engine is first started, or any other time the converter temperature falls below its optimum operating temperature, the efficiency of the catalyst is reduced. As such, it is desirable to reduce the amount of time during which the catalyst is outside of its optimum operating temperature range to improve overall conversion efficiency.
Electronic thermactor air (ETA) systems have been used to increase the rate at which the catalyst reaches its operating temperature from a relatively cold ambient temperature. The ETA systems introduce excess air (and therefore oxygen) into the exhaust stream causing the catalyst to reach its operating temperature more quickly. However, these systems require additional hardware, such as pumps and valves, to provide the excess air to the exhaust stream. It is thus desirable to reduce the amount of time the catalyst is below its optimum operating temperature by providing excess air to the catalyst without the cost and complexity associated with the prior art systems and methods.